Monogamy, or restrictions by law to one wife, is no part of the economy of Heaven among men. Such a system was commenced by the founders of the Roman empire. That empire was founded on the banks of the Tiber by wandering brigands. When these robbers founded the city of Rome, it was evident to them that their success in attaining a balance of power with their neighbours, depended upon introducing females into their body politic, so they stole them from the Sabines, who were near neighbours. The scarcity of women gave existence to laws restricting one wife to one man. Rome became the mistress of the world, and introduced this order of monogamy wherever her sway was acknowledged. Thus this monogamic order of marriage, so esteemed by modern Christians as a holy sacrament and divine institution, is nothing but a system established by a set of robbers. The Congress of the United States have lately passed a law to punish polygamy in the Territories of the United States and in other places over which they have exclusive jurisdiction. In doing this, they have undertaken to dictate the Almighty in his revelations to his people, and those who handle edged tools, unless they are skillful, are apt to cut their fingers; and those who hand out insult to the Great I Am, in the end, are apt to get more than they have spoken for. Why do we believe in and practise polygamy? Because the Lord introduced it to his servants in a revelation given to Joseph Smith, and the Lord's servants have always practiced it. '"And is that religion popular in heaven?'" It is the only popular religion there, for this is the religion of Abraham, and, unless we do the works of Abraham, we are not Abraham's seed and heirs according to promise.
[Source: Journal of Discourses. Liverpool, England, 1853-86. 9:318-323, in The Complete Discourses of Brigham Young, Ed. Richard S. Van Wagoner, Smith-Pettit Foundation, Salt Lake City (2009), http://bit.ly/BY-discourses]